This is a randomized trial of immediate versus delayed endoscopic diagnosis in the patient with upper gastrointestinal bleeding. End-points include survival, emergency surgery, transfusion requirement, management decisions and patient tolerance. The study will continue until 300 patients have been randomized. Those patients who are actively bleeding at the time of entry into the study are also randomized to receive intravenous vasopressin or placebo. The purpose is to determine whether this drug stops bleeding and prevents the need for surgery in this subset of critically ill patients.